Abstract

The effectiveness of any aquifer rehabilitation program involving free phase liquid hydrocarbon reflects a comprehensive understanding of geologic and hydrogeologic conditions. As with many aquifer rehabilitation programs, limitations including waste water handling capabilities and site specific factors all play key roles in the success of such programs. The occurrence and recoverability of several FPLH pools beneath an active refinery site have been investigated and evaluated over a period of six years. The refinery site is situated on the Los Angeles coastal plain, California, and is immediately underlain by a sequence of unconsolidated, stratified, laterally discontinuous fluvial deposits comprising Recent deposits and the Lakewood Formation. Five separate FPLH pools of dissimilar product types and comprising over a million barrels of refined product in total volume are estimated to occur under shallow perched and water table conditions. Product types include gasoline, diesel, kerosene and mixed heavy gas oil.

Over 200,000 barrels of FPLH have been recovered to date via two primary but different recovery and mitigation strategies. In relatively high permeability zones, a system consisting of four two-pump recovery wells is employed. Water produced is not treated and reinjected into the aquifer from which it was originally withdrawn through a network of injection wells. The injection wells serve to create a barrier to offsite migration, enhance the hydraulic gradient towards a recovery well, and dispose of water which would otherwise require treatment and subsequent discharge. In relatively low permeability areas, a network of one-pump recovery wells is employed in which the FPLH generated is routed to an oil/water separator, from which water is piped to an on-site waste water treatment facility.